fix(#1098): guard generate-claude-md against clobbering hand-crafted files; redirect default to .claude/CLAUDE.md (#1118)

/gsd-new-project wrote a repo-root CLAUDE.md full of broad project docs,
overwriting/diluting a hand-crafted instruction file. --force was parsed but
silently dropped, and nothing guarded an existing non-GSD file.

- Guard: an existing instruction file with no `<!-- GSD:<section>-start` markers
  (hand-crafted) is left untouched; report action:"skipped". --force (now wired
  through CmdGenerateClaudeMdOptions) overwrites intentionally. The marker check
  uses /<!-- GSD:[a-z]+-start/ so a file merely documenting GSD syntax is safe.
- Redirect: the Claude-family default output is now ./.claude/CLAUDE.md (a valid
  auto-loaded project-memory location) instead of repo-root ./CLAUDE.md. Aligned
  across the handler default, config-defaults.manifest.json, buildNewProjectConfig,
  the config template, new-project.md, and cmdGenerateClaudeProfile; advisory
  read-CLAUDE.md hints in plan-phase/quick/profile-user updated. Codex still
  writes AGENTS.md.

Closes #1098

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

.changeset/1098-generate-claude-md-guard-redirect.md

@@ -0,0 +1,5 @@
+---
+type: Fixed
+pr: 1118
+---
+**`gsd-tools generate-claude-md` no longer clobbers a hand-crafted `CLAUDE.md`, and defaults the Claude-runtime output to `./.claude/CLAUDE.md`** — `/gsd-new-project` wrote a repo-root `CLAUDE.md` full of broad project documentation, overwriting/diluting an existing hand-authored instruction file. Now: (1) an existing instruction file that contains no GSD section markers (a hand-crafted file) is left untouched and the command reports `action: "skipped"` — pass `--force` to overwrite intentionally (the flag was already parsed but ignored); (2) the default output for Claude-family runtimes is `./.claude/CLAUDE.md` (a valid project-scoped memory location) instead of repo-root `./CLAUDE.md`, so generated content does not pollute a repo-root file. The config default (`claude_md_path`), the project config template, and the new-project workflow are aligned to the new location. Codex projects still write `AGENTS.md`. (#1098)